fix empty string insertion bug

src/Util/ID.js

@@ -11,6 +11,10 @@ export default class ID {
     return id !== null && id.user === this.user && id.clock === this.clock
   }
   lessThan (id) {
-    return this.user < id.user || (this.user === id.user && this.clock < id.clock)
+    if (id.constructor === ID) {
+      return this.user < id.user || (this.user === id.user && this.clock < id.clock)
+    } else {
+      return false
+    }
   }
 }